Dual SIM dual standby user equipment rat selection

ABSTRACT

A UE determines a set of RATs available in accordance with a first subscriber identity associated with a first network and a second subscriber identity associated with a second network. When the set includes a first RAT accessing a base station in the first network, a second RAT accessing a base station in the second network, and a third RAT accessing an access point of a WLAN, the UE selects, in a first performance configuration, the first RAT to establish a first call under the first subscriber identity. The UE further communicates, under the first subscriber identity, with a first IMS server of the first network through the first RAT to establish the first call. The UE maintains, under the second subscriber identity, a connection with a second IMS server of the second network through the first RAT or the third RAT when the first call is active.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application claims the benefits of U.S. Provisional ApplicationSer. No. 62/570,688, entitled “DSDS UE SUPPORT DA” and filed on Oct. 11,2017, which is expressly incorporated by reference herein in theirentirety.

BACKGROUND Field

The present disclosure relates generally to communication systems, andmore particularly, to techniques for selecting a radio access technology(RAT) on a dual SIM dual standby user equipment (UE).

Background

The statements in this section merely provide background informationrelated to the present disclosure and may not constitute prior art.

Wireless communication systems are widely deployed to provide varioustelecommunication services such as telephony, video, data, messaging,and broadcasts. Typical wireless communication systems may employmultiple-access technologies capable of supporting communication withmultiple users by sharing available system resources. Examples of suchmultiple-access technologies include code division multiple access(CDMA) systems, time division multiple access (TDMA) systems, frequencydivision multiple access (FDMA) systems, orthogonal frequency divisionmultiple access (OFDMA) systems, single-carrier frequency divisionmultiple access (SC-FDMA) systems, and time division synchronous codedivision multiple access (TD-SCDMA) systems.

These multiple access technologies have been adopted in varioustelecommunication standards to provide a common protocol that enablesdifferent wireless devices to communicate on a municipal, national,regional, and even global level. An example telecommunication standardis 5G New Radio (NR). 5G NR is part of a continuous mobile broadbandevolution promulgated by Third Generation Partnership Project (3GPP) tomeet new requirements associated with latency, reliability, security,scalability (e.g., with Internet of Things (IoT)), and otherrequirements. Some aspects of 5G NR may be based on the 4G Long TermEvolution (LTE) standard. There exists a need for further improvementsin 5G NR technology. These improvements may also be applicable to othermulti-access technologies and the telecommunication standards thatemploy these technologies.

SUMMARY

The following presents a simplified summary of one or more aspects inorder to provide a basic understanding of such aspects. This summary isnot an extensive overview of all contemplated aspects, and is intendedto neither identify key or critical elements of all aspects nordelineate the scope of any or all aspects. Its sole purpose is topresent some concepts of one or more aspects in a simplified form as aprelude to the more detailed description that is presented later.

In an aspect of the disclosure, a method, a computer-readable medium,and an apparatus are provided. The apparatus may be a UE. The UEdetermines a set of radio access technologies (RATs) available to the UEin accordance with a first subscriber identity associated with a firstnetwork and a second subscriber identity associated with a secondnetwork. When the set includes a first RAT accessing a base station inthe first network, a second RAT accessing a base station in the secondnetwork, and a third RAT accessing an access point of a wireless localarea network (WLAN), the UE selects, in a first performanceconfiguration, the first RAT to establish a first call under the firstsubscriber identity. The UE further communicates, under the firstsubscriber identity, with a first IP Multimedia Subsystem (IMS) serverof the first network through the first RAT to establish the first call.The UE maintains, under the second subscriber identity, a connectionwith a second IMS server of the second network through the first RAT orthe third RAT when the first call is active.

To the accomplishment of the foregoing and related ends, the one or moreaspects comprise the features hereinafter fully described andparticularly pointed out in the claims. The following description andthe annexed drawings set forth in detail certain illustrative featuresof the one or more aspects. These features are indicative, however, ofbut a few of the various ways in which the principles of various aspectsmay be employed, and this description is intended to include all suchaspects and their equivalents.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram illustrating an example of a wireless communicationssystem and an access network.

FIG. 2 is a diagram illustrating a base station in communication with aUE in an access network.

FIG. 3 illustrates an example logical architecture of a distributedaccess network.

FIG. 4 illustrates an example physical architecture of a distributedaccess network.

FIG. 5 is a diagram showing an example of a DL-centric subframe.

FIG. 6 is a diagram showing an example of an UL-centric subframe.

FIG. 7 is a diagram 700 illustrating communications between a UE andanother UE through different radio access technologies (RATs).

FIG. 8 is a diagram showing an example of an enhanced IMS serviceavailability maintenance mechanism (EISAMM).

FIG. 9 is a diagram illustrating techniques of EISAMM and intelligenttraffic steering mechanism (ITSM).

FIG. 10 is a diagram an example of EISAMM and ITSM.

FIG. 11 is a diagram illustrating techniques of wireless communicationof the UE.

FIG. 12 is another diagram illustrating techniques of wirelesscommunication of the UE.

FIG. 13 is yet another diagram illustrating techniques of wirelesscommunication of the UE.

FIG. 14 is also a diagram illustrating techniques of wirelesscommunication of the UE.

FIG. 15 is a flow chart illustrating a method (process) of wirelesscommunication of a UE.

FIG. 16 is a flow chart illustrating a method (process) of wirelesscommunication of a UE.

FIG. 17 is a flow chart illustrating a method (process) of wirelesscommunication of a UE.

FIG. 18 is a flow chart illustrating a method (process) of wirelesscommunication of a UE.

FIG. 19 is a flow chart illustrating a method (process) of wirelesscommunication of a UE.

FIG. 20 is a flow chart illustrating a method (process) of wirelesscommunication of a UE.

FIG. 21 is a flow chart illustrating a method (process) of wirelesscommunication of a UE.

FIG. 22 is a flow chart illustrating a method (process) of wirelesscommunication of a UE.

FIG. 23 is a flow chart illustrating a method (process) of wirelesscommunication of a UE.

FIG. 24 is a flow chart illustrating a method (process) of wirelesscommunication of a UE.

FIG. 25 is a conceptual data flow diagram illustrating the data flowbetween different components/means in an exemplary apparatus.

FIG. 26 is a diagram illustrating an example of a hardwareimplementation for an apparatus employing a processing system.

DETAILED DESCRIPTION

The detailed description set forth below in connection with the appendeddrawings is intended as a description of various configurations and isnot intended to represent the only configurations in which the conceptsdescribed herein may be practiced. The detailed description includesspecific details for the purpose of providing a thorough understandingof various concepts. However, it will be apparent to those skilled inthe art that these concepts may be practiced without these specificdetails. In some instances, well known structures and components areshown in block diagram form in order to avoid obscuring such concepts.

Several aspects of telecommunication systems will now be presented withreference to various apparatus and methods. These apparatus and methodswill be described in the following detailed description and illustratedin the accompanying drawings by various blocks, components, circuits,processes, algorithms, etc. (collectively referred to as “elements”).These elements may be implemented using electronic hardware, computersoftware, or any combination thereof. Whether such elements areimplemented as hardware or software depends upon the particularapplication and design constraints imposed on the overall system.

By way of example, an element, or any portion of an element, or anycombination of elements may be implemented as a “processing system” thatincludes one or more processors. Examples of processors includemicroprocessors, microcontrollers, graphics processing units (GPUs),central processing units (CPUs), application processors, digital signalprocessors (DSPs), reduced instruction set computing (RISC) processors,systems on a chip (SoC), baseband processors, field programmable gatearrays (FPGAs), programmable logic devices (PLDs), state machines, gatedlogic, discrete hardware circuits, and other suitable hardwareconfigured to perform the various functionality described throughoutthis disclosure. One or more processors in the processing system mayexecute software. Software shall be construed broadly to meaninstructions, instruction sets, code, code segments, program code,programs, subprograms, software components, applications, softwareapplications, software packages, routines, subroutines, objects,executables, threads of execution, procedures, functions, etc., whetherreferred to as software, firmware, middleware, microcode, hardwaredescription language, or otherwise.

Accordingly, in one or more example embodiments, the functions describedmay be implemented in hardware, software, or any combination thereof. Ifimplemented in software, the functions may be stored on or encoded asone or more instructions or code on a computer-readable medium.Computer-readable media includes computer storage media. Storage mediamay be any available media that can be accessed by a computer. By way ofexample, and not limitation, such computer-readable media can comprise arandom-access memory (RAM), a read-only memory (ROM), an electricallyerasable programmable ROM (EEPROM), optical disk storage, magnetic diskstorage, other magnetic storage devices, combinations of theaforementioned types of computer-readable media, or any other mediumthat can be used to store computer executable code in the form ofinstructions or data structures that can be accessed by a computer.

FIG. 1 is a diagram illustrating an example of a wireless communicationssystem and an access network 100. The wireless communications system(also referred to as a wireless wide area network (WWAN)) includes basestations 102, UEs 104, and a core network (e.g. Evolved Packet Core(EPC), 5G CN) 160. The base stations 102 may include macro cells (highpower cellular base station) and/or small cells (low power cellular basestation). The macro cells include base stations. The small cells includefemtocells, picocells, and microcells.

The base stations 102 (collectively referred to as Evolved UniversalMobile Telecommunications System (UMTS) Terrestrial Radio Access Network(E-UTRAN)) interface with the core network 160 through backhaul links132 (e.g., S1 interface). In addition to other functions, the basestations 102 may perform one or more of the following functions:transfer of user data, radio channel ciphering and deciphering,integrity protection, header compression, mobility control functions(e.g., handover, dual connectivity), inter-cell interferencecoordination, connection setup and release, load balancing, distributionfor non-access stratum (NAS) messages, NAS node selection,synchronization, radio access network (RAN) sharing, multimediabroadcast multicast service (MBMS), subscriber and equipment trace, RANinformation management (RIM), paging, positioning, and delivery ofwarning messages. The base stations 102 may communicate directly orindirectly (e.g., through the core network 160) with each other overbackhaul links 134 (e.g., X2 interface). The backhaul links 134 may bewired or wireless.

The base stations 102 may wirelessly communicate with the UEs 104. Eachof the base stations 102 may provide communication coverage for arespective geographic coverage area 110. There may be overlappinggeographic coverage areas 110. For example, the small cell 102′ may havea coverage area 110′ that overlaps the coverage area 110 of one or moremacro base stations 102. A network that includes both small cell andmacro cells may be known as a heterogeneous network. A heterogeneousnetwork may also include Home Evolved Node Bs (eNBs) (HeNBs), which mayprovide service to a restricted group known as a closed subscriber group(CSG). The communication links 120 between the base stations 102 and theUEs 104 may include uplink (UL) (also referred to as reverse link)transmissions from a UE 104 to a base station 102 and/or downlink (DL)(also referred to as forward link) transmissions from a base station 102to a UE 104. The communication links 120 may use multiple-input andmultiple-output (MIMO) antenna technology, including spatialmultiplexing, beamforming, and/or transmit diversity. The communicationlinks may be through one or more carriers. The base stations 102/UEs 104may use spectrum up to Y MHz (e.g., 5, 10, 15, 20, 100 MHz) bandwidthper carrier allocated in a carrier aggregation of up to a total of YxMHz (x component carriers) used for transmission in each direction. Thecarriers may or may not be adjacent to each other. Allocation ofcarriers may be asymmetric with respect to DL and UL (e.g., more or lesscarriers may be allocated for DL than for UL). The component carriersmay include a primary component carrier and one or more secondarycomponent carriers. A primary component carrier may be referred to as aprimary cell (PCell) and a secondary component carrier may be referredto as a secondary cell (SCell).

The wireless communications system may further include a Wi-Fi accesspoint (AP) 150 in communication with Wi-Fi stations (STAs) 152 viacommunication links 154 in a 5 GHz unlicensed frequency spectrum. Whencommunicating in an unlicensed frequency spectrum, the STAs 152/AP 150may perform a clear channel assessment (CCA) prior to communicating inorder to determine whether the channel is available.

The small cell 102′ may operate in a licensed and/or an unlicensedfrequency spectrum. When operating in an unlicensed frequency spectrum,the small cell 102′ may employ NR and use the same 5 GHz unlicensedfrequency spectrum as used by the Wi-Fi AP 150. The small cell 102′,employing NR in an unlicensed frequency spectrum, may boost coverage toand/or increase capacity of the access network.

The gNodeB (gNB) 180 may operate in millimeter wave (mmW) frequenciesand/or near mmW frequencies in communication with the UE 104. When thegNB 180 operates in mmW or near mmW frequencies, the gNB 180 may bereferred to as an mmW base station. Extremely high frequency (EHF) ispart of the RF in the electromagnetic spectrum. EHF has a range of 30GHz to 300 GHz and a wavelength between 1 millimeter and 10 millimeters.Radio waves in the band may be referred to as a millimeter wave. NearmmW may extend down to a frequency of 3 GHz with a wavelength of 100millimeters. The super high frequency (SHF) band extends between 3 GHzand 30 GHz, also referred to as centimeter wave. Communications usingthe mmW/near mmW radio frequency band has extremely high path loss and ashort range. The mmW base station 180 may utilize beamforming 184 withthe UE 104 to compensate for the extremely high path loss and shortrange.

The core network 160 may include a Mobility Management Entity (MME) 162,other MMEs 164, a Serving Gateway 166, a Multimedia Broadcast MulticastService (MBMS) Gateway 168, a Broadcast Multicast Service Center (BM-SC)170, and a Packet Data Network (PDN) Gateway 172. The MME 162 may be incommunication with a Home Subscriber Server (HSS) 174. The MME 162 isthe control node that processes the signaling between the UEs 104 andthe core network 160. Generally, the MME 162 provides bearer andconnection management. All user Internet protocol (IP) packets aretransferred through the Serving Gateway 166, which itself is connectedto the PDN Gateway 172. The PDN Gateway 172 provides UE IP addressallocation as well as other functions. The PDN Gateway 172 and the BM-SC170 are connected to the IP Services 176. The IP Services 176 mayinclude the Internet, an intranet, an IP Multimedia Subsystem (IMS), aPS Streaming Service (PSS), and/or other IP services. The BM-SC 170 mayprovide functions for MBMS user service provisioning and delivery. TheBM-SC 170 may serve as an entry point for content provider MBMStransmission, may be used to authorize and initiate MBMS Bearer Serviceswithin a public land mobile network (PLMN), and may be used to scheduleMBMS transmissions. The MBMS Gateway 168 may be used to distribute MBMStraffic to the base stations 102 belonging to a Multicast BroadcastSingle Frequency Network (MBSFN) area broadcasting a particular service,and may be responsible for session management (start/stop) and forcollecting eMBMS related charging information.

The base station may also be referred to as a gNB, Node B, evolved NodeB (eNB), an access point, a base transceiver station, a radio basestation, a radio transceiver, a transceiver function, a basic serviceset (BSS), an extended service set (ESS), or some other suitableterminology. The base station 102 provides an access point to the corenetwork 160 for a UE 104. Examples of UEs 104 include a cellular phone,a smart phone, a session initiation protocol (SIP) phone, a laptop, apersonal digital assistant (PDA), a satellite radio, a globalpositioning system, a multimedia device, a video device, a digital audioplayer (e.g., MP3 player), a camera, a game console, a tablet, a smartdevice, a wearable device, a vehicle, an electric meter, a gas pump, atoaster, or any other similar functioning device. Some of the UEs 104may be referred to as IoT devices (e.g., parking meter, gas pump,toaster, vehicles, etc.). The UE 104 may also be referred to as astation, a mobile station, a subscriber station, a mobile unit, asubscriber unit, a wireless unit, a remote unit, a mobile device, awireless device, a wireless communications device, a remote device, amobile subscriber station, an access terminal, a mobile terminal, awireless terminal, a remote terminal, a handset, a user agent, a mobileclient, a client, or some other suitable terminology.

In certain aspects, the UE 104 includes, among other components, adecision component 192, a communication management component 194, and ahandover component 198. The decision component 192 determine a set ofRATs available to the UE 702 in accordance with a first subscriberidentity associated with a first network and a second subscriberidentity associated with a second network. The decision component 192determines whether the set includes a first RAT accessing a base stationin the first network, a second RAT accessing a base station in thesecond network, and a third RAT accessing an access point of a WLAN.When the set includes a first RAT accessing a base station in the firstnetwork, a second RAT accessing a base station in the second network,and a third RAT accessing an access point of a WLAN, the communicationmanagement component 194 communicates, under the first subscriberidentity, with a first IP Multimedia Subsystem (IMS) server of the firstnetwork through the first RAT to establish the first call. Thecommunication management component 194 maintains, under the secondsubscriber identity, a connection with a second IMS server of the secondnetwork through the first RAT or the third RAT when the first call isactive.

FIG. 2 is a block diagram of a base station 210 in communication with aUE 250 in an access network. In the DL, IP packets from the core network160 may be provided to a controller/processor 275. Thecontroller/processor 275 implements layer 3 and layer 2 functionality.Layer 3 includes a radio resource control (RRC) layer, and layer 2includes a packet data convergence protocol (PDCP) layer, a radio linkcontrol (RLC) layer, and a medium access control (MAC) layer. Thecontroller/processor 275 provides RRC layer functionality associatedwith broadcasting of system information (e.g., MIB, SIBs), RRCconnection control (e.g., RRC connection paging, RRC connectionestablishment, RRC connection modification, and RRC connection release),inter radio access technology (RAT) mobility, and measurementconfiguration for UE measurement reporting; PDCP layer functionalityassociated with header compression/decompression, security (ciphering,deciphering, integrity protection, integrity verification), and handoversupport functions; RLC layer functionality associated with the transferof upper layer packet data units (PDUs), error correction through ARQ,concatenation, segmentation, and reassembly of RLC service data units(SDUs), re-segmentation of RLC data PDUs, and reordering of RLC dataPDUs; and MAC layer functionality associated with mapping betweenlogical channels and transport channels, multiplexing of MAC SDUs ontotransport blocks (TBs), demultiplexing of MAC SDUs from TBs, schedulinginformation reporting, error correction through HARQ, priority handling,and logical channel prioritization.

The transmit (TX) processor 216 and the receive (RX) processor 270implement layer 1 functionality associated with various signalprocessing functions. Layer 1, which includes a physical (PHY) layer,may include error detection on the transport channels, forward errorcorrection (FEC) coding/decoding of the transport channels,interleaving, rate matching, mapping onto physical channels,modulation/demodulation of physical channels, and MIMO antennaprocessing. The TX processor 216 handles mapping to signalconstellations based on various modulation schemes (e.g., binaryphase-shift keying (BPSK), quadrature phase-shift keying (QPSK),M-phase-shift keying (M-PSK), M-quadrature amplitude modulation(M-QAM)). The coded and modulated symbols may then be split intoparallel streams. Each stream may then be mapped to an OFDM subcarrier,multiplexed with a reference signal (e.g., pilot) in the time and/orfrequency domain, and then combined together using an Inverse FastFourier Transform (IFFT) to produce a physical channel carrying a timedomain OFDM symbol stream. The OFDM stream is spatially precoded toproduce multiple spatial streams. Channel estimates from a channelestimator 274 may be used to determine the coding and modulation scheme,as well as for spatial processing. The channel estimate may be derivedfrom a reference signal and/or channel condition feedback transmitted bythe UE 250. Each spatial stream may then be provided to a differentantenna 220 via a separate transmitter 218TX. Each transmitter 218TX maymodulate an RF carrier with a respective spatial stream fortransmission.

At the UE 250, each receiver 254RX receives a signal through itsrespective antenna 252. Each receiver 254RX recovers informationmodulated onto an RF carrier and provides the information to the receive(RX) processor 256. The TX processor 268 and the RX processor 256implement layer 1 functionality associated with various signalprocessing functions. The RX processor 256 may perform spatialprocessing on the information to recover any spatial streams destinedfor the UE 250. If multiple spatial streams are destined for the UE 250,they may be combined by the RX processor 256 into a single OFDM symbolstream. The RX processor 256 then converts the OFDM symbol stream fromthe time-domain to the frequency domain using a Fast Fourier Transform(FFT). The frequency domain signal comprises a separate OFDM symbolstream for each subcarrier of the OFDM signal. The symbols on eachsubcarrier, and the reference signal, are recovered and demodulated bydetermining the most likely signal constellation points transmitted bythe base station 210. These soft decisions may be based on channelestimates computed by the channel estimator 258. The soft decisions arethen decoded and deinterleaved to recover the data and control signalsthat were originally transmitted by the base station 210 on the physicalchannel. The data and control signals are then provided to thecontroller/processor 259, which implements layer 3 and layer 2functionality.

The controller/processor 259 can be associated with a memory 260 thatstores program codes and data. The memory 260 may be referred to as acomputer-readable medium. In the UL, the controller/processor 259provides demultiplexing between transport and logical channels, packetreassembly, deciphering, header decompression, and control signalprocessing to recover IP packets from the core network 160. Thecontroller/processor 259 is also responsible for error detection usingan ACK and/or NACK protocol to support HARQ operations.

Similar to the functionality described in connection with the DLtransmission by the base station 210, the controller/processor 259provides RRC layer functionality associated with system information(e.g., MIB, SIBs) acquisition, RRC connections, and measurementreporting; PDCP layer functionality associated with headercompression/decompression, and security (ciphering, deciphering,integrity protection, integrity verification); RLC layer functionalityassociated with the transfer of upper layer PDUs, error correctionthrough ARQ, concatenation, segmentation, and reassembly of RLC SDUs,re-segmentation of RLC data PDUs, and reordering of RLC data PDUs; andMAC layer functionality associated with mapping between logical channelsand transport channels, multiplexing of MAC SDUs onto TBs,demultiplexing of MAC SDUs from TBs, scheduling information reporting,error correction through HARQ, priority handling, and logical channelprioritization.

Channel estimates derived by a channel estimator 258 from a referencesignal or feedback transmitted by the base station 210 may be used bythe TX processor 268 to select the appropriate coding and modulationschemes, and to facilitate spatial processing. The spatial streamsgenerated by the TX processor 268 may be provided to different antenna252 via separate transmitters 254TX. Each transmitter 254TX may modulatean RF carrier with a respective spatial stream for transmission. The ULtransmission is processed at the base station 210 in a manner similar tothat described in connection with the receiver function at the UE 250.Each receiver 218RX receives a signal through its respective antenna220. Each receiver 218RX recovers information modulated onto an RFcarrier and provides the information to a RX processor 270.

The controller/processor 275 can be associated with a memory 276 thatstores program codes and data. The memory 276 may be referred to as acomputer-readable medium. In the UL, the controller/processor 275provides demultiplexing between transport and logical channels, packetreassembly, deciphering, header decompression, control signal processingto recover IP packets from the UE 250. IP packets from thecontroller/processor 275 may be provided to the core network 160. Thecontroller/processor 275 is also responsible for error detection usingan ACK and/or NACK protocol to support HARQ operations.

New radio (NR) may refer to radios configured to operate according to anew air interface (e.g., other than Orthogonal Frequency DivisionalMultiple Access (OFDMA)-based air interfaces) or fixed transport layer(e.g., other than Internet Protocol (IP)). NR may utilize OFDM with acyclic prefix (CP) on the uplink and downlink and may include supportfor half-duplex operation using time division duplexing (TDD). NR mayinclude Enhanced Mobile Broadband (eMBB) service targeting widebandwidth (e.g., 80 MHz beyond), millimeter wave (mmW) targeting highcarrier frequency (e.g., 60 GHz), massive MTC (mMTC) targetingnon-backward compatible MTC techniques, and/or mission criticaltargeting ultra-reliable low latency communications (URLLC) service.

A single component carrier bandwidth of 100 MHZ may be supported. In oneexample, NR resource blocks (RBs) may span 12 sub-carriers with asub-carrier bandwidth of 60 kHz over a 0.125 ms duration or a bandwidthof 15 kHz over a 0.5 ms duration. Each radio frame may consist of 20 or80 subframes (or NR slots) with a length of 10 ms. Each subframe mayindicate a link direction (i.e., DL or UL) for data transmission and thelink direction for each subframe may be dynamically switched. Eachsubframe may include DL/UL data as well as DL/UL control data. UL and DLsubframes for NR may be as described in more detail below with respectto FIGS. 5 and 6.

The NR RAN may include a central unit (CU) and distributed units (DUs).A NR BS (e.g., gNB, 5G Node B, Node B, transmission reception point(TRP), access point (AP)) may correspond to one or multiple BSs. NRcells can be configured as access cells (ACells) or data only cells(DCells). For example, the RAN (e.g., a central unit or distributedunit) can configure the cells. DCells may be cells used for carrieraggregation or dual connectivity and may not be used for initial access,cell selection/reselection, or handover. In some cases DCells may nottransmit synchronization signals (SS) in some cases DCells may transmitSS. NR BSs may transmit downlink signals to UEs indicating the celltype. Based on the cell type indication, the UE may communicate with theNR BS. For example, the UE may determine NR BSs to consider for cellselection, access, handover, and/or measurement based on the indicatedcell type.

FIG. 3 illustrates an example logical architecture 300 of a distributedRAN, according to aspects of the present disclosure. A 5G access node306 may include an access node controller (ANC) 302. The ANC may be acentral unit (CU) of the distributed RAN 300. The backhaul interface tothe next generation core network (NG-CN) 304 may terminate at the ANC.The backhaul interface to neighboring next generation access nodes(NG-ANs) may terminate at the ANC. The ANC may include one or more TRPs308 (which may also be referred to as BSs, NR BSs, Node Bs, 5G NBs, APs,or some other term). As described above, a TRP may be usedinterchangeably with “cell.”

The TRPs 308 may be a distributed unit (DU). The TRPs may be connectedto one ANC (ANC 302) or more than one ANC (not illustrated). Forexample, for RAN sharing, radio as a service (RaaS), and servicespecific AND deployments, the TRP may be connected to more than one ANC.A TRP may include one or more antenna ports. The TRPs may be configuredto individually (e.g., dynamic selection) or jointly (e.g., jointtransmission) serve traffic to a UE.

The local architecture of the distributed RAN 300 may be used toillustrate fronthaul definition. The architecture may be defined thatsupport fronthauling solutions across different deployment types. Forexample, the architecture may be based on transmit network capabilities(e.g., bandwidth, latency, and/or jitter). The architecture may sharefeatures and/or components with LTE. According to aspects, the nextgeneration AN (NG-AN) 310 may support dual connectivity with NR. TheNG-AN may share a common fronthaul for LTE and NR.

The architecture may enable cooperation between and among TRPs 308. Forexample, cooperation may be preset within a TRP and/or across TRPs viathe ANC 302. According to aspects, no inter-TRP interface may beneeded/present.

According to aspects, a dynamic configuration of split logical functionsmay be present within the architecture of the distributed RAN 300. ThePDCP, RLC, MAC protocol may be adaptably placed at the ANC or TRP.

FIG. 4 illustrates an example physical architecture of a distributed RAN400, according to aspects of the present disclosure. A centralized corenetwork unit (C-CU) 402 may host core network functions. The C-CU may becentrally deployed. C-CU functionality may be offloaded (e.g., toadvanced wireless services (AWS)), in an effort to handle peak capacity.A centralized RAN unit (C-RU) 404 may host one or more ANC functions.Optionally, the C-RU may host core network functions locally. The C-RUmay have distributed deployment. The C-RU may be closer to the networkedge. A distributed unit (DU) 406 may host one or more TRPs. The DU maybe located at edges of the network with radio frequency (RF)functionality.

FIG. 5 is a diagram 500 showing an example of a DL-centric subframe. TheDL-centric subframe may include a control portion 502. The controlportion 502 may exist in the initial or beginning portion of theDL-centric subframe. The control portion 502 may include variousscheduling information and/or control information corresponding tovarious portions of the DL-centric subframe. In some configurations, thecontrol portion 502 may be a physical DL control channel (PDCCH), asindicated in FIG. 5. The DL-centric subframe may also include a DL dataportion 504. The DL data portion 504 may sometimes be referred to as thepayload of the DL-centric subframe. The DL data portion 504 may includethe communication resources utilized to communicate DL data from thescheduling entity (e.g., UE or BS) to the subordinate entity (e.g., UE).In some configurations, the DL data portion 504 may be a physical DLshared channel (PDSCH).

The DL-centric subframe may also include a common UL portion 506. Thecommon UL portion 506 may sometimes be referred to as an UL burst, acommon UL burst, and/or various other suitable terms. The common ULportion 506 may include feedback information corresponding to variousother portions of the DL-centric subframe. For example, the common ULportion 506 may include feedback information corresponding to thecontrol portion 502. Non-limiting examples of feedback information mayinclude an ACK signal, a NACK signal, a HARQ indicator, and/or variousother suitable types of information. The common UL portion 506 mayinclude additional or alternative information, such as informationpertaining to random access channel (RACH) procedures, schedulingrequests (SRs), and various other suitable types of information.

As illustrated in FIG. 5, the end of the DL data portion 504 may beseparated in time from the beginning of the common UL portion 506. Thistime separation may sometimes be referred to as a gap, a guard period, aguard interval, and/or various other suitable terms. This separationprovides time for the switch-over from DL communication (e.g., receptionoperation by the subordinate entity (e.g., UE)) to UL communication(e.g., transmission by the subordinate entity (e.g., UE)). One ofordinary skill in the art will understand that the foregoing is merelyone example of a DL-centric subframe and alternative structures havingsimilar features may exist without necessarily deviating from theaspects described herein.

FIG. 6 is a diagram 600 showing an example of an UL-centric subframe.The UL-centric subframe may include a control portion 602. The controlportion 602 may exist in the initial or beginning portion of theUL-centric subframe. The control portion 602 in FIG. 6 may be similar tothe control portion 502 described above with reference to FIG. 5. TheUL-centric subframe may also include an UL data portion 604. The UL dataportion 604 may sometimes be referred to as the pay load of theUL-centric subframe. The UL portion may refer to the communicationresources utilized to communicate UL data from the subordinate entity(e.g., UE) to the scheduling entity (e.g., UE or BS). In someconfigurations, the control portion 602 may be a physical DL controlchannel (PDCCH).

As illustrated in FIG. 6, the end of the control portion 602 may beseparated in time from the beginning of the UL data portion 604. Thistime separation may sometimes be referred to as a gap, guard period,guard interval, and/or various other suitable terms. This separationprovides time for the switch-over from DL communication (e.g., receptionoperation by the scheduling entity) to UL communication (e.g.,transmission by the scheduling entity). The UL-centric subframe may alsoinclude a common UL portion 606. The common UL portion 606 in FIG. 6 maybe similar to the common UL portion 606 described above with referenceto FIG. 6. The common UL portion 606 may additionally or alternativelyinclude information pertaining to channel quality indicator (CQI),sounding reference signals (SRSs), and various other suitable types ofinformation. One of ordinary skill in the art will understand that theforegoing is merely one example of an UL-centric subframe andalternative structures having similar features may exist withoutnecessarily deviating from the aspects described herein.

In some circumstances, two or more subordinate entities (e.g., UEs) maycommunicate with each other using sidelink signals. Real-worldapplications of such sidelink communications may include public safety,proximity services, UE-to-network relaying, vehicle-to-vehicle (V2V)communications, Internet of Everything (IoE) communications, IoTcommunications, mission-critical mesh, and/or various other suitableapplications. Generally, a sidelink signal may refer to a signalcommunicated from one subordinate entity (e.g., UE1) to anothersubordinate entity (e.g., UE2) without relaying that communicationthrough the scheduling entity (e.g., UE or BS), even though thescheduling entity may be utilized for scheduling and/or controlpurposes. In some examples, the sidelink signals may be communicatedusing a licensed spectrum (unlike wireless local area networks, whichtypically use an unlicensed spectrum).

Recently there has been a propagation of calls using Voice over LongTerm Evolution (VOLTE) standards. That, combined with the continuedincrease in cellular network telecommunications traffic, hasincentivized some service providers to offer calling through Wi-Ficonnections in accordance with the various IEEE 802.11 standards. SuchWi-Fi offloading, as it is called, enables telecommunications calls anddata from a UE to be offloaded from the cellular network to the internetfor transport from the UE to the termination destination point and viceversa. Such Wi-Fi networks may be either generally secure, operatorcontrolled networks, known as trusted networks, or generally unsecured,publicly accessible Wi-Fi networks through public hotspots and the like,known as untrusted networks.

Besides, the IP Multimedia Subsystem (IMS) is technology that merges theinternet with the cellular world. It makes internet technology such asthe web, email, instant messaging, user presence, video conferencing andso forth available in nearly any location. The IMS is a key element in3G (and beyond) architecture that makes it possible to provideubiquitous access to all services that the internet provides. Forexample, it enables one to access their favorite web pages, read theiremail, watch a movie or take part in the video conference wherever oneis by simply using a mobile device and accessing the desired services.

Generally, the IMS combines the latest trends in packet switchtechnology and circuit switch technology to make a mobile internetavailable. It also creates a common platform to develop variousmultimedia services and creates a mechanism to boost margins for serviceproviders due to extra usage of mobile packet switch networks. There arevarious protocols used in the IMS which include the session controlprotocol, and a SIP as well as other protocols known to those of skillin the art that are utilized for providing the multimedia services. TheIMS architecture is a collection of functions linked by standardizedinterfaces. Most venders follow the IMS architecture closely andimplement each function in a single node although other nodes may beused.

FIG. 7 is a diagram 700 illustrating communications between a UE 702 andanother UE 703 through different mobile network with corresponding radioaccess technologies (RATs). Subscriber identity module (SIM), widelyknown as a SIM card, is an integrated circuit that is intended tosecurely store the international mobile subscriber identity (IMSI)number and its related key, which are used by a network to identify andauthenticate subscribers on a UE like the UE 702 and 703. A device mayhave multiple subscriber identity module (SIM). In this example, the UE702, a multi-SIM device, has two SIMs: SIM1 702-1 and SIM2 702-2.Typically, different SIMs correspond to different cellular networkoperators. In this example, the SIM1 702-1 corresponds to a mobilenetwork 791 while SIM 2 702-2 corresponds to a mobile network 792. Inother words, the UE 702 can operates as a subscriber of the mobilenetwork 791 utilizing identity information provided by the SIM1 702-1.Alternatively, the UE 702 can operates as a subscriber of the mobilenetwork 792 utilizing identity information provided by the SIM1 702-2.The mobile network 791 may include, among other components, a basestation 704-1, a serving gateway 706-1, a PDN gateway 708-1, a mobilitymanagement entity (MME) 710-1 and a policy and charging rules function(PCRF) 712-1. The mobile network 791 is associated with an IMS service714-1. The PDN gateway 708-1 is connected to both the IMS service 714-1and the PDN 720. Similarly, the mobile network 792 includes, among othercomponents, a base station 704-2, a serving gateway 706-2, a PDN gateway708-2, a MME 710-2 and a PCRF 712-2. The mobile network 792 isassociated with an IMS service 714-2. The PDN gateway 708-2 is connectedto both the IMS service 714-2 and the PDN 720. On the other hand, the UE703 is connected, in the same way, to an IMS service 714-3 and the PDN720. The IMS service 714-1, the IMS service 714-2, and the IMS services714-3 can communicate with each other.

Therefore, the UE 702 and the UE 703 can communicate with each other viavarious routes. For example, the UE 702 can communicate with the UE 703in an IMS call via the mobile network 791 corresponding to SIM1 702-1.More specifically, the signaling path may be from the UE 702 through thebase station 704-1, the serving gateway 706-1, the PDN gateway 708-1,the IMS service 714-1, the IMS services 714-3, eventually to the UE 703,and vice versa. The data traffic path may be from the UE 702 through thebase station 704-1, the serving gateway 706-1, the PDN gateway 708-1,the PDN 720, eventually to the UE 703, and vice versa.

In another example, the UE 702 can communicate with the UE 703 in an IMScall via the mobile network 792 corresponding to SIM2 702-2. Morespecifically, the signaling path may be from the UE 702 through the basestation 704-2, the serving gateway 706-2, the PDN gateway 708-2, the IMSservice 714-2, the IMS services 714-3, eventually to the UE 703, andvice versa. The data traffic path may be from the UE 702 through thebase station 704-2, the serving gateway 706-2, the PDN gateway 708-2,the PDN 720, eventually to the UE 703, and vice versa.

In yet another example, the UE 702 may use an untrusted access network(such as a WLAN network 716, which may be a Wi-Fi network) tocommunicate with the PDN gateway 708-2 of the mobile network 792 througha security gateway such as an ePDG 718. The ePDG 718 is one of theelements of core network.

The ePDG 718 plays a role of a security node for an untrusted accessnetwork (such as a WLAN network 716). In various configurations, the UE702 may establish a secure tunnel over the WLAN network 716 with theePDG 718. With the help of the ePDG 718 and the WLAN network 716, the UE702 can communicate with the UE 703 via both the WLAN network 716 andthe PDN gateway 708-2 of the mobile network 792 corresponding to SIM2702-2. More specifically, the signaling path is from the UE 702 throughWLAN network 716, the ePDG 718, the PDN gateway 708-2, the IMS service714-2, the IMS services 714-3, eventually to the UE 703, and vice versa.The data traffic path is from the UE 702 through WLAN network 716, theePDG 718, the PDN gateway 708-2, the PDN 720, eventually to the UE 703,and vice versa. As such, a call with the UE 702 through the mobilenetwork 791 or the mobile network 792 can be offloaded to an IMS callthrough the WLAN network 716.

FIG. 8 is a diagram 800 showing an example of an enhanced IMS serviceavailability maintenance mechanism (EISAMM). An application layer 802employs EISAMM 804 to make IMS calls. The UE 702 may use three RATs: aRAT-1 826, a RAT-2 822, and a RAT-3 824. Under the subscriber identityof SIM2 702-2, the UE 702 can access the mobile network 792 using theRAT-2 822, and therefore be connected to the IMS service 714-2 or thePDN 720. More specifically, EISAMM 804 may establish an IMS call througha non access stratum (NAS) layer 806, an access stratum (AS) layer 808,and cellular modem and radio 810 of the UE 702 that can access themobile network 792. The NAS layer 806 is a functional layer in wirelesstelecom protocol stacks between the core network (including, among otherthings, a serving gateway 706-2, a PDN gateway 708-2, a MME 710-2 and aPCRF 712-2) and the UE 702. The AS 808 is a functional layer in awireless telecom protocol stacks between radio network (including, amongother things, a base station 704-2) and the UE 702. The cellular modemand radio 810 is a module includes, among other things, modem, radiofrequency components such as antennas, power amplifiers. While the RAT-1826 is owned by the mobile network 791 and the RAT-2 822 is owned by themobile network 792, RAT-1 and RAT-2 can be the same “Radio accesstechnology” (e.g., E-UTRA, UTRA, NR . . . etc).

Under the subscriber identity of SIM1 702-1, the UE 702 can also accessthe mobile network 791 using the RAT-1 826, and therefore be connectedto the IMS service 714-1 or the PDN 720. More specifically, EISAMM 804may establish an IMS call through a non access stratum (NAS) layer 818,an access stratum (AS) layer 820, and the cellular modem and radio 810of the UE 702 that can access the mobile network 791. The NAS layer 818is a functional layer in wireless telecom protocol stacks between thecore network (including, among other things, a serving gateway 706-1, aPDN gateway 708-1, a MME 710-1 and a PCRF 712-1) and the UE 702. The AS820 is a functional layer in a wireless telecom protocol stacks betweenradio network (including, among other things, a base station 704-1) andthe UE 702. The cellular modem and radio 810 is a module including,among other things, modem, radio frequency components such as antennas,power amplifiers.

Moreover, in this example, under the subscriber identity of SIM2 702-2,the UE 702 can access the mobile network 792 through the WLAN network716 using the RAT-3 824, and therefore be connected to the IMS service714-2 or the PDN 720. More specifically, EISAMM 804 may establish an IMScall through a WLAN driver 812, a WLAN firmware 814, and a Wi-Fi modemand radio 816 of the UE 702 that can access the WLAN network 716. TheWi-Fi modem and radio 816 is a module including, among other things,modem, radio frequency components such as antennas, power amplifiers.Therefore, EISAMM 804 can select a feasible RAT to establish an IMS callon the UE 702.

FIG. 9 is a diagram 900 illustrating techniques of an enhanced IMSservice availability maintenance mechanism (EISAMM) and intelligenttraffic steering mechanism (ITSM). One or more UEs may be connected toone or more of the mobile network 791, the mobile network 792, and theWLAN network 716. Further, the mobile network 791 has a coverage 908,the mobile network 792 has a coverage 910, and the WLAN network 716 hasa coverage 912. Depending on the coverage of these three networks, thearea can be divided into seven sub-areas. In other words, there areseven scenarios depending on the location of UE 702.

In the first scenario 914, a UE (e.g., the UE 702) is only within thecoverage 908 of the mobile network 791. Similarly, in the third scenario918, a UE is only within the coverage 910 of the mobile network 792. Inthe second scenario 916, a UE is within the coverage 908 and 910 of boththe mobile network 791 and the mobile network 792. In each of the threescenarios, i.e., the first scenario 914, the second scenario 916, thethird scenario 918, only mobile network(s) (e.g., the mobile network 791and/or the mobile network 792) is/are available to a UE, and the WLANnetwork 716 is not available. Therefore, the UE can only connect to theIMS service 714-1 and/or 714-2 via mobile networks.

In the fourth scenario 920, a UE is within the coverage 908 of themobile network 791 and the coverage 912 of the WLAN network 716.Similarly, in the sixth scenario, a UE is within the coverage 910 of themobile network 792 and the coverage 912 of the WLAN network 716. Whilein the fifth scenario 922, a UE is within the coverage 908 of the mobilenetwork 791, the coverage 910 of the mobile network 792, and thecoverage 912 of the WLAN network 716. In each of the three scenarios,i.e., the fourth scenario 920, the fifth scenario 922, and the sixthscenario 924, at least one mobile network 791 and/or 792 as well as aWLAN network 716 are available. Therefore, a UE can connect to the IMSservice 714-1 and/or 714-2 via either the mobile network(s) 791 and/or792 or the WLAN network 716.

Finally, in the seventh scenario 926, a UE is only within the coverage912 of the WLAN network 716. In other words, no cellular network (e.g.,the mobile network 791 and/or the mobile network 792) is available tothe UE. Therefore, a UE may only connect to the IMS service 714-1 and/or714-2 via the WLAN network 716.

EISAMM is a mechanism that can select an appropriate RAT for accessing aparticular network for establish or maintain an IMS. In each of theseven scenarios of this example, EISAMM may select an appropriate RAT toaccess the mobile network 791, the mobile network 792, and the WLANnetwork 716.

On the other hand, ITSM may enhance active call performance by handover.For example, in the second scenario 916, where the UE 702 is within boththe coverage 908 of the mobile network 791 and the coverage 910 of themobile network 792, ITSM can transfer connection to an IMS service(e.g., the IMS service 714-1) from one RAT to another. Morespecifically, under the subscriber identity of SIM2 702-2, ITSM cantransfer connection to the IMS service from via the mobile network 792to via the mobile network 791. In another example, in the fifth scenario922, the UE 702 is within the coverage 908, 910, and 912. Therefore,under the subscriber identity of SIM2 702-2, ITSM can transferconnection to the IMS service 714-2 from via the mobile network 792 tovia the mobile network 791 or via the WLAN network 716. The choice ofIMS service connection depends on a selection schemes which will bedetailed below.

FIG. 10 is a diagram 1000 illustrating an example of EISAMM and ITSM.“A” means Option A, where a SIM is used to access the own network of theSIM. “C” means Option C, where a SIM is used to access a peer network ofthe SIM. “B” means Option B, where a SIM is used to access a networkthrough a WLAN.

In the first scenario 914, a UE (e.g., the UE 702) is only within thecoverage 908 of the mobile network 791. Therefore, SIM1 702-1 is used inOption A and SIM2 702-2 is used in Option C. In other words, SIM1 702-1is used to access its own network (the mobile network 791). SIM2 is usedto access a peer network (the mobile network 791) of SIM2.

Similarly, in the third scenario 918, a UE is only within the coverage910 of the mobile network 792. Therefore, SIM1 702-1 is used in Option Cand SIM2 702-2 is used in Option A. In other words, SIM1 702-1 is usedto access a peer network (the mobile network 792), while SIM2 702-2 isused to access its own network (the mobile network 792).

In the second scenario 916, a UE is within the coverage 908 and 910.Therefore, SIM1 702-1 is used in Option A and Option C, and SIM2 702-2is used in Option A and Option C as well. In other words, both SIM1702-1 and SIM2 702-2 can be used to access their respective own networksor peer networks. If SIM1 702-1 is used to have a voice call, EISAMM 804will select Option A for SIM1 702-1 since using its own network (themobile network 791) can provide a better voice call performance.Accordingly, SIM2 702-2 will end up using Option C. In other words, SIM2702-2 is used to access a peer network (the mobile network 791). Inother words, SIM1 702-1 and SIM2 702-2 are both used to access themobile network 791.

In the fourth scenario 920, a UE is within the coverage 908 and 912.Therefore, SIM1 702-1 is used in Option A and Option B, while SIM2 702-2is used in Option B and Option C. In other words, SIM1 702-1 can be usesto access either its own network or a WLAN network, while SIM2 can beused to access either a peer network or a WLAN network. If SIM1 702-1 isused to have a voice call, EISAMM 804 will select Option A for SIM1702-1 since using own network (the mobile network 791) can provide abetter voice call performance. Accordingly, SIM2 702-2 is used in eitherOption B or Option C. In other words, SIM2 702-2 is used to accesseither the WLAN network 716 or a peer network (the mobile network 791).In other words, SIM1 702-1 and SIM2 702-2 are both used to access themobile network 791. Since there are two options for SIM2 702-2, ITSM canbe employed to enhance active call performance by handover.

Similarly in the sixth scenario 924, a UE is within the coverage 910 and912. Therefore, SIM1 702-1 is used in Option C and Option B, while SIM2702-2 is used in Option A and Option B. In other words, SIM1 702-1 canbe used to access either a peer network or a WLAN network, while SIM2702-2 can be uses to access either its own network or a WLAN network. IfSIM1 702-1 is used to have a voice call, EISAMM 804 will select eitherOption B or Option C for SIM1 702-1 since using its own network is notavailable here. Accordingly, SIM2 702-2 is used in either Option A orOption B. In other words, SIM2 702-2 is used to access either the WLANnetwork 716 or its own network (i.e., the mobile network 792). Sincethere are two options for both SIM1 702-1 and SIM2 702-2, ITSM can beemployed to enhance active call performance by handover.

In the fifth scenario 922, a UE is within the coverage 908, 910, and912. Therefore, both SIM1 702-1 and SIM2 702-2 have Option A, Option B,and Option C. In other words, both SIM1 702-1 and SIM2 702-2 can be usesto access their respective own networks, peer networks, or a WLANnetwork. If SIM1 702-1 is used to have a voice call, EISAMM 804 willselect Option A for SIM1 702-1 since using own network can provide abetter voice call performance. Accordingly, SIM2 702-2 is used in eitherOption B or Option C. In other words, SIM2 is used to access either theWLAN network 716 or a peer network (i.e., the mobile network 791). Inother words, SIM1 702-1 and SIM2 702-2 can both be uses to access themobile network 791. Since there are two options for SIM2 702-2, ITSM canbe employed to enhance active call performance by handover.

In the seventh scenario 926, a UE is within the coverage 912. Therefore,both SIM1 702-1 and SIM2 702-2 are used in Option B. In other words,both SIM1 702-1 and SIM2 702-2 can be used to access their networks viathe WLAN network 716.

FIG. 11 is a diagram 1100 illustrating techniques of wirelesscommunication of the UE 702. SIM1 1102 has two available RATs: SIM1RAT-OPT-A 1106 and SIM1 RAT-OPT-B 1108, where SIM1 RAT-OPT-A 1106 refersto a RAT accessing the SIM's own network, i.e., the mobile network 791;and SIM1 RAT-OPT-B 1108 refers to a RAT accessing the WLAN network 716.SIM2 1104 has three available RATs: SIM2 RAT-OPT-A 1110, SIM2 RAT-OPT-B1112, and SIM2 RAT-OPT-C 1114, where SIM2 RAT-OPT-A 1110 refers to a RATof the SIM's own network, i.e., the mobile network 792; SIM2 RAT-OPT-B1111 refers to a RAT accessing the WLAN network 716; and SIM2 RAT-OPT-C1114 refers to a RAT accessing a peer network of the SIM, i.e., themobile network 791.

At beginning 1116, the initial state is that IMS service is idle. Morespecifically, at 1118, SIM1 1102 is connected via SIM1 RAT-OPT-A 1106,while at 1120, SIM2 1104 is connected via SIM2 RAT-OPT-A 1110. In otherwords, both SIM1 1102 and SIM2 1104 are using its own network in initialstate 1116 where IMS service is idle.

Then SIM1 1102 becomes call active at 1122. Since using its own networkcan provide a better voice call performance than using the WLAN network716, EISAMM will select SIM1 RAT-OPT-A 1106 to establish a call, at1124. As to SIM2 1104, there are two alternatives: alternative one 1126and alternative two 1132.

In alternative one 1126, only mobile network is available, at 1128. Inother words, SIM2 RAT-OPT-A 1110 and SIM2 RAT-OPT-C 1114 are available,and SIM2 RAT-OPT-B 1112 is not available. In this situation, SIM2 1104is connected via SIM2 RAT-OPT-C 1114. In other words, SIM2 1104 is usingpeer network, i.e., the mobile network 791.

In alternative two 1132, both mobile network and the WLAN network 716are available, at 1134. SIM2 1104 may access ePDG 718 via peer network(the mobile network 791) via the, at 1136. In this case, SIM2 1104 isconnected via SIM2 RAT-OPT-C 1114, at 1138.

SIM2 1104 may also access ePDG 718 via the WLAN network 716, at 1140.More specifically, at 1142, SIM2 1104 connection is handed over to SIM2RAT-OPT-B 1112. More specifically, at 1144, devices first authenticateeach other and establish a security association using a protocol calledInternet Key Exchange version 2 (IKEv2), and encryption and integrityprotection are then implemented using the Internet Protocol Security(IPSec) Encapsulating Security Payload. At 1146, IPsec tunnel setup iscompleted. At 1148, SIM2 1104 is connected via ePDG 718. Then, at 1150,a 3GPP bearer is released. In summary, the UE 702 can hand overconnection of the SIM2 1104 to the WLAN network 716 by following 3GPP TS23.402 flow.

IMS service may have different characteristics under differentconditions. For example, IMS service connected via a SIM's own mobilenetwork, corresponding to Option A, has the characteristic of stablewireless resource with quality of service (QoS) guarantee. IMS serviceconnected via a peer mobile network of the SIM, corresponding to OptionC, has the characteristic of stable wireless resource but without QoSguarantee. IMS service connected via the WLAN network 716, correspondingto Option B, has the characteristics of less power consumption and lesscost from unlicensed band (2.4 GHz/5 GHz), contention-based wirelessresource, and without QoS guarantee.

For a dual SIM dual standby (DSDS) UE under the second scenario 916, thefourth scenario 920, the fifth scenario 922, and the sixth scenario 924,as mentioned above and illustrated in FIG. 9, ITSM selects a proper RAT,based on at least one of the following group of requirements: callquality, a cost to make the first call, a power consumption of the UE702, and a handover rate. More specifically, in a performance centricsituation, best voice/video quality is desired, and generally IMSservice (e.g., the IMS service 714-1 or 714-2) with active callgenerally should stay on the mobile network. In a cost centricsituation, reducing data plan cost for the voice/video call is desired,and generally IMS service (e.g., the IMS service 714-1 or 714-2) withactive call should stay on the WLAN network 716. In a power centricsituation, reducing power consumption of the UE 702 is desired. In amobility centric situation, reducing handover occurring rate is desired.In a hybrid situation, ITSM can combine all the requirements orperformance indicator mentioned above with different weights to select apreferred RAT. The allocation of weights are flexible as needed. Itshould be noted other requirements or performance indicators can beemployed based on consumer need.

FIG. 12 is a diagram 1200 illustrating techniques of wirelesscommunication of the UE 702. SIM1 1202 has two available RATs: SIM1RAT-OPT-A 1206 and SIM1 RAT-OPT-C 1208, where SIM1 702-1 RAT-OPT-A 1206refers to a RAT accessing the SIM's own network, i.e., the mobilenetwork 791; and SIM1 702-1 RAT-OPT-C 1208 refers to a RAT accessing apeer network of the SIM, i.e., the mobile network 792. SIM2 1204 has twoavailable RATs: SIM2 RAT-OPT-A 1210 and SIM2 RAT-OPT-C 1212, where SIM2RAT-OPT-A 1210 refers to a RAT accessing the SIM's own network, i.e.,the mobile network 792; SIM2 RAT-OPT-C 1212 refers to a RAT accessing apeer network of the SIM, i.e., the mobile network 791.

At beginning 1214, a SIM1 voice-over-LTE (VoLTE) call is active. Morespecifically, at 1216, a call is active on SIM1 via the mobile network791, while at 1218, SIM2 is connected via SIM2 RAT-OPT-C 1212. In otherwords, both SIM1 1202 and SIM2 1204 are using the mobile network 791 ininitial state 1214 where SIM1 VoLTE call is active.

Then SIM2 mobile terminating (MT) call occurs at 1220. Morespecifically, at 1222, a SIP invite is sent via SIM1 702-1 internet PDN.

Then at 1224, the UE 702 can hold SIM1 call and pick up SIM2 call, sothat SIM2 call can become an active call. More specifically, aperformance centric mechanism is applied at 1226, and SIM2 call becomesactive via SIM2 RAT-OPT-A 1210, at 1244. In other words, SIM2 call isvia the mobile network 792. It should be noted that the sequencesbetween 1226 and 1244 can be changed. In other words, SIM2 call canbecome active via SIM2 RAT-OPT-A 1210 first at 1244, then a performancecentric mechanism is applied at 1226.

More specifically, applying performance centric mechanism 1226 includesthat SIM2 IMS service is transferred to the IMS service 714-2, at 1228.In other words, SIM2 call is using its own network, i.e., the mobilenetwork 792, and therefore, a better voice/video quality can beachieved. More specifically, at 1230, a PDN handover request is sent tothe mobile network 792. Since SIM1 call is held, the UE 702 can reserveenough radio resource to serve SIM2 PDN handover request over the mobilenetwork 792. Then, at 1232, SIM2 1204 is connected to the IMS service714-2. Then, at 1234, a 3GPP bearer is released.

Optionally, connection of SIM1 1202 is handed over to SIM1 RAT-OPT-C1208. In other words, SIM1 702-1 is using peer network, i.e., the mobilenetwork 792. More specifically, at 1238, a PDN handover request is sentto the mobile network 792. Then, at 1240, SIM1 1202 is connected to theIMS service 714-2. Then, at 1242, a 3GPP bearer is released.

FIG. 13 is a diagram 1300 illustrating techniques of wirelesscommunication of the UE 702. SIM1 1302 has three available RATs: SIM1RAT-OPT-A 1306, SIM1 RAT-OPT-B 1308, and SIM1 RAT-OPT-C 1310, where SIM1RAT-OPT-A 1306 refers to a RAT accessing the SIM's own network, i.e.,the mobile network 791; SIM1 RAT-OPT-B 1308 refers to a RAT accessingthe WLAN network 716; and SIM1 RAT-OPT-C 1310 refers to a RAT accessinga peer network of the SIM, i.e., the mobile network 792. SIM2 1304 hastwo available RATs: SIM2 RAT-OPT-A 1312, and SIM2 RAT-OPT-B 1314, whereSIM2 RAT-OPT-A 1312 refers to a RAT accessing the SIM's own network,i.e., the mobile network 792; and SIM2 RAT-OPT-B 1314 refers to a RATaccessing the WLAN network 716.

At beginning 1316, a SIM1 call is active. More specifically, at 1318,SIM1 call is active on SIM1 RAT-OPT-A 1306, while at 1320, SIM2 isconnected via SIM2 RAT-OPT-B 1313. In other words, SIM1 1302 is usingown network (the mobile network 791) while SIM2 1304 is using the WLANnetwork 716.

Then SIM2 voice-over-WiFi (VoWifi) mobile terminating call occurs at1322. More specifically, at 1324, a SIP invite is sent.

Then at 1326, UE can hold SIM1 call and pick up SIM2 call, so that SIM2call can become an active call. More specifically, a performance centricmechanism is applied at 1328, and SIM2 call becomes active on SIM2RAT-OPT-A 1312, at 1354. It should be noted that the sequences between1328 and 1354 can be changed. In other words, SIM2 call can becomeactive on SIM2 RAT-OPT-A 1312 first at 1354, then a performance centricmechanism is applied at 1328.

More specifically, applying performance centric mechanism 1328 includesthat connection of SIM1 1302 is handed over to SIM1 RAT-OPT-B 1308 at1330. In other words, SIM1 call is using the WLAN network 716, andtherefore, mobile network resource is released. More specifically, at1332, devices first authenticate each other and establish a securityassociation using a protocol called Internet Key Exchange version 2(IKEv2), and encryption and integrity protection are then implementedusing the Internet Protocol Security (IPSec) Encapsulating SecurityPayload. At 1334, IPsec tunnel setup is completed. Then, at 1336, a 3GPPbearer is released.

To keep active call performance, SIM2 call need to be transferred tomobile network, i.e., the mobile network 792. Thus, at 1338, connectionof SIM2 1304 is handed over to SIM2 RAT-OPT-A 1312. More specifically,at 1340, a PDN handover request is sent. Then, SIM2 1304 is connected tothe IMS service 714-2 at 1342. Then, a non-3GPP bearer is released at1344.

Optionally, connection of SIM1 1302 is handed over to SIM1 RAT-OPT-C1310. In other words, SIM1 1302 is using peer network, i.e., the mobilenetwork 792. More specifically, at 1348, a PDN handover request is sentto the mobile network 792. Then, at 1350, SIM1 1302 is connected to theIMS service 714-2. Then, at 1352, a non-3GPP bearer is released.

FIG. 14 is a diagram 1400 illustrating techniques of wirelesscommunication of the UE 702. SIM1 1402 has two available RATs: SIM1RAT-OPT-A 1406 and SIM1 RAT-OPT-B 1408, where SIM1 RAT-OPT-A 1406 refersto a RAT accessing the SIM's own network, i.e., the mobile network 791;and SIM1 RAT-OPT-B 1408 refers to a RAT accessing the WLAN network 716.SIM2 1404 has two available RATs: SIM2 RAT-OPT-A 1410 and SIM2 RAT-OPT-B1412, where SIM2 RAT-OPT-A 1410 refers to a RAT accessing the SIM's ownnetwork, i.e., the mobile network 792; SIM2 RAT-OPT-B 1412 refers to aRAT accessing the WLAN network 716.

At beginning 1414, the initial state is that IMS service is idle. Morespecifically, at 1416, SIM1 1402 is connected via SIM1 RAT-OPT-A 1406,while at 1418, SIM2 1404 is connected via SIM2 RAT-OPT-A 1410. In otherwords, both SIM1 1402 and SIM2 1404 are using its own network in initialstate 1414 where IMS service is idle.

Then SIM1 call becomes active at 1420. More specifically, at 1422, a SIPinvite is sent.

Then at 1424, a cost centric mechanism is applied. For example, in thesituation of a video call, WLAN is usually preferred for cost-savingpurpose. More specifically, at 1428, devices first authenticate eachother and establish a security association using a protocol calledInternet Key Exchange version 2 (IKEv2), and encryption and integrityprotection are then implemented using the Internet Protocol Security(IPSec) Encapsulating Security Payload. At 1430, IPsec tunnel setup iscompleted. At 1432, SIM1 1402 is connected to the IMS service 714-1 viaan ePDG (like the ePDG 718). Then, at 1434, a 3GPP bearer is released.In summary, the UE 702 can hand over SIM1 call to the WLAN network 716according to a cost centric mechanism.

Additionally, in a hybrid RAT selection situation, each available RAT isevaluated by giving each concerned requirement or performance indicatora weight and calculate the corresponding total score of each RAT. Anactive call then will be transferred to the RAT with the highest totalscore, and that RAT is called a preferred RAT. The performance centricmechanism and the cost centric mechanism mentioned above can be regardedas typical examples of a general hybrid RAT selection situation. Inother words, a general hybrid RAT selection can be flexible in selectingconcerned requirement or performance indicator and allocating weightsthereof as needed.

More specifically, an average of each performance indicator over time isfirst calculated. Then, each desired performance indicator will beassigned a number 1, and other performance indicators will be assigned anumber 0. Finally, multiply the average of each performance indicatorover time by the assigned number (0 or 1, representing whether aspecific performance indicator is desired to be used in evaluation) aswell as their weights, and add the results up. In this way, each RAT canget a weighted mean score as to both time and various performanceindicators. This is an intelligent, adaptive mechanism.

FIG. 15 is a flow chart 1500 illustrating a method (process) of wirelesscommunication of a UE 702. The method may be performed by a UE (e.g.,the UE 702, the apparatus 2502/2502′). At operation 1502, the UE 702determine a set of RATs available to the UE 702 in accordance with afirst subscriber identity (e.g., SIM1 702-1) associated with a firstnetwork (e.g., the mobile network 791) and a second subscriber identity(e.g., SIM2 702-2) associated with a second network (e.g., the mobilenetwork 792).

At operation 1504, the UE 702 determines whether the set includes afirst RAT (e.g., the RAT-1 826) accessing a base station (e.g., the basestation 704-1) in the first network, a second RAT (e.g., the RAT-2 822)accessing a base station (e.g., the base station 704-2) in the secondnetwork, and a third RAT (e.g., the RAT-3 824) accessing an access pointof a WLAN (e.g., the WLAN network 716). If the set includes the firstRAT accessing a base station in the first network, a second RATaccessing a base station in the second network, and a third RATaccessing an access point of a WLAN, then the method (process) proceedsto operation 1506, otherwise the method (process) ends.

At operation 1506, the UE 702 selects, in a first performanceconfiguration, the first RAT to establish a first call under the firstsubscriber identity (e.g., the SIM1 702-1). In certain configurations,the first RAT is selected based on at least one of a call quality, acost to make the first call, a power consumption of the UE, and ahandover rate.

At operation 1508, the UE 702 maintains, under the first subscriberidentity, a connection with the first IMS server (e.g., the IMS service714-1) through the first RAT.

At operation 1510, the UE 702 maintains, under the second subscriberidentity, the connection with the second IMS server (e.g., the IMSservice 714-2) through the second RAT (e.g., the RAT-2 822).

At operation 1512, the UE 702 communicates, under the first subscriberidentity, with a first IMS server (e.g., the IMS service 714-1) of thefirst network through the first RAT to establish the first call.

At operation 1514, the UE 702 hands over the connection with the secondIMS server (e.g., the IMS service 714-2) from the second RAT to thefirst RAT or the third RAT.

The operation 1514 is followed by the operation 1602 in FIG. 16 below.

FIG. 16 is a flow chart 1600 illustrating a method (process) of wirelesscommunication of a UE 702. The method may be performed by a UE (e.g.,the UE 702, the apparatus 2502/2502′). At operation 1602, the UE 702maintains, under the second subscriber identity, a connection with asecond IMS server (e.g., the IMS service 714-2) of the second networkthrough the first RAT (e.g., the RAT-1 826) or the third RAT (e.g., theRAT-3 824) when the first call is active.

At operation 1604, the UE 702 receives, through the first RAT and underthe first subscriber identity, a call invitation to establish the firstcall.

At operation 1606, the UE 702 selects, in a second performanceconfiguration, the third RAT to establish the first call under the firstsubscriber identity.

At operation 1608, the UE 702 hands over the connection under the firstsubscriber identity with the first IMS server from the first RAT to thethird RAT (e.g., RAT-3 824).

At operation 1610, the UE 702 communicate, under the first subscriberidentity, with the first IMS server through the third RAT (e.g., RAT-3824) to establish the first call.

At operation 1612, the UE 702 determines whether the connection underthe second subscriber identity with the second IMS server is maintainedthrough the third RAT (e.g., RAT-3 824). If the connection under thesecond subscriber identity with the second IMS server is maintainedthrough the third RAT (e.g., RAT-3 824), then proceed to operation 1614,otherwise the method (process) ends.

At operation 1614, the UE 702 receives a call invitation to establish asecond call under the second subscriber identity through the third RAT(e.g., RAT-3 824).

The operation 1614 is followed by the operation 1702 in FIG. 17 below.

FIG. 17 is a flow chart 1700 illustrating a method (process) of wirelesscommunication of a UE 702. The method may be performed by a UE (e.g.,the UE 702, the apparatus 2502/2502′). At operation 1702, the UE 702holds the first call.

At operation 1704, the UE 702 hands over the connection under the secondsubscriber identity with the second IMS server from the third RAT (e.g.,RAT-3 824) to the second RAT (e.g., RAT-2 822).

At operation 1706, the UE 702 communicates, under the second subscriberidentity, with the second IMS server through the second RAT (e.g., RAT-2822) to establish the second call.

At operation 1708, the UE 702 hands over the holding of the first callfrom the first RAT to the third RAT.

FIG. 18 is a flow chart 1800 illustrating a method (process) of wirelesscommunication of a UE 702. The method may be performed by a UE (e.g.,the UE 702, the apparatus 2502/2502′). At operation 1802, the UE 702determine a set of RATs available to the UE 702 in accordance with afirst subscriber identity (e.g., SIM1 702-1) associated with a firstnetwork (e.g., the mobile network 791) and a second subscriber identity(e.g., SIM2 702-2) associated with a second network (e.g., the mobilenetwork 792).

At operation 1804, the UE 702 determines whether the set includes thefirst RAT. If the set includes the first RAT, then the method (process)proceeds to operation 1806, otherwise the method (process) ends.

At operation 1806, the UE 702 communicates, under the first subscriberidentity, with the first IMS server through the first RAT to establishthe first call.

At operation 1808, the UE 702 maintains, under the second subscriberidentity, a connection with the second IMS server through the first RAT(e.g., RAT-1 826) when the first call is active.

FIG. 19 is a flow chart 1900 illustrating a method (process) of wirelesscommunication of a UE 702. The method may be performed by a UE (e.g.,the UE 702, the apparatus 2502/2502′). At operation 1902, the UE 702determine a set of RATs available to the UE 702 in accordance with afirst subscriber identity (e.g., SIM1 702-1) associated with a firstnetwork (e.g., the mobile network 791) and a second subscriber identity(e.g., SIM2 702-2) associated with a second network (e.g., the mobilenetwork 792).

At operation 1904, the UE 702 determines whether the set includes thefirst RAT and the second RAT. If the set includes the first RAT and thesecond RAT, then the method (process) proceeds to operation 1006,otherwise the method (process) ends.

At operation 1906, the UE 702 communicates, under the first subscriberidentity, with the first IMS server through the first RAT to establishthe first call.

At operation 1908, the UE 702 maintains, under the second subscriberidentity, a connection with the second IMS server through the first RAT(e.g., RAT-1 826) when the first call is active.

At operation 1910, the UE 702 receives a call invitation to establish asecond call under the second subscriber identity through the first RAT(e.g., RAT-1 826).

At operation 1912, the UE 702 holds the first call.

At operation 1914, the UE 702 hands over the connection under the secondsubscriber identity with the second IMS server from the first RAT (e.g.,RAT-1 826) to the second RAT (e.g., RAT-2 822).

The operation 1914 is followed by operation 2002 in FIG. 20 below.

FIG. 20 is a flow chart 1900 illustrating a method (process) of wirelesscommunication of a UE 702. The method may be performed by a UE (e.g.,the UE 702, the apparatus 2502/2502′). At operation 2002, the UE 702communicates, under the second subscriber identity, with the second IMSserver through the second RAT to establish the second call.

At operation 2004, the UE 702 hands over the holding of the first callfrom the first RAT to the second RAT.

FIG. 21 is a flow chart 1800 illustrating a method (process) of wirelesscommunication of a UE 702. The method may be performed by a UE (e.g.,the UE 702, the apparatus 2502/2502′). At operation 2102, the UE 702determine a set of RATs available to the UE 702 in accordance with afirst subscriber identity (e.g., SIM1 702-1) associated with a firstnetwork (e.g., the mobile network 791) and a second subscriber identity(e.g., SIM2 702-2) associated with a second network (e.g., the mobilenetwork 792).

At operation 2104, the UE 702 determines whether the set includes thesecond RAT. If the set includes the second RAT, then the method(process) proceeds to operation 2106, otherwise the method (process)ends.

At operation 2106, the UE 702 communicates, under the first subscriberidentity, with the first IMS server through the second RAT to establishthe first call.

At operation 2108, the UE 702 maintains, under the second subscriberidentity, a connection with the second IMS server through the second RAT(e.g., RAT-2 822) when the first call is active.

FIG. 22 is a flow chart 2200 illustrating a method (process) of wirelesscommunication of a UE 702. The method may be performed by a UE (e.g.,the UE 702, the apparatus 2502/2502′). At operation 2202, the UE 702determine a set of RATs available to the UE 702 in accordance with afirst subscriber identity (e.g., SIM1 702-1) associated with a firstnetwork (e.g., the mobile network 791) and a second subscriber identity(e.g., SIM2 702-2) associated with a second network (e.g., the mobilenetwork 792).

At operation 2204, the UE 702 determines whether the set includes thefirst RAT and the third RAT. If the set includes the first RAT and thethird RAT, then the method (process) proceeds to operation 2206,otherwise the method (process) ends.

At operation 2206, the UE 702 communicates, under the first subscriberidentity, with the first IMS server through the first RAT to establishthe first call.

At operation 2208, the UE 702 maintains, under the second subscriberidentity, a connection with the second IMS server through the first RAT(e.g., RAT-1 826) or the second RAT (e.g., RAT-2 822) when the firstcall is active.

FIG. 23 is a flow chart 2300 illustrating a method (process) of wirelesscommunication of a UE 702. The method may be performed by a UE (e.g.,the UE 702, the apparatus 2502/2502′). At operation 2302, the UE 702determine a set of RATs available to the UE 702 in accordance with afirst subscriber identity (e.g., SIM1 702-1) associated with a firstnetwork (e.g., the mobile network 791) and a second subscriber identity(e.g., SIM2 702-2) associated with a second network (e.g., the mobilenetwork 792).

At operation 2304, the UE 702 determines whether the set includes thesecond RAT and the third RAT. If the set includes the second RAT and thethird RAT, then the method (process) proceeds to operation 2306,otherwise the method (process) ends.

At operation 2306, the UE 702 communicates, under the first subscriberidentity, with the first IMS server through the second RAT or the thirdRAT (e.g., RAT-3 824) to establish the first call.

At operation 2308, the UE 702 maintains, under the second subscriberidentity, a connection with the second IMS server through the second RAT(e.g., RAT-2 822) or the third RAT (e.g., RAT-3 824) when the first callis active.

FIG. 23 is a flow chart 2300 illustrating a method (process) of wirelesscommunication of a UE 702. The method may be performed by a UE (e.g.,the UE 702, the apparatus 2502/2502′). At operation 2302, the UE 702determine a set of RATs available to the UE 702 in accordance with afirst subscriber identity (e.g., SIM1 702-1) associated with a firstnetwork (e.g., the mobile network 791) and a second subscriber identity(e.g., SIM2 702-2) associated with a second network (e.g., the mobilenetwork 792).

At operation 2304, the UE 702 determines whether the set includes thesecond RAT and the third RAT. If the set includes the second RAT and thethird RAT, then the method (process) proceeds to operation 2306,otherwise the method (process) ends.

At operation 2306, the UE 702 communicates, under the first subscriberidentity, with the first IMS server through the second RAT or the thirdRAT (e.g., RAT-3 824) to establish the first call.

At operation 2308, the UE 702 maintains, under the second subscriberidentity, a connection with the second IMS server through the second RAT(e.g., RAT-2 822) or the third RAT (e.g., RAT-3 824) when the first callis active.

FIG. 24 is a flow chart 2400 illustrating a method (process) of wirelesscommunication of a UE 702. The method may be performed by a UE (e.g.,the UE 702, the apparatus 2502/2502′). At operation 2402, the UE 702determine a set of RATs available to the UE 702 in accordance with afirst subscriber identity (e.g., SIM1 702-1) associated with a firstnetwork (e.g., the mobile network 791) and a second subscriber identity(e.g., SIM2 702-2) associated with a second network (e.g., the mobilenetwork 792).

At operation 2404, the UE 702 determines whether the set includes thethird RAT. If the set includes the third RAT, then the method (process)proceeds to operation 2406, otherwise the method (process) ends.

At operation 2406, the UE 702 communicates, under the first subscriberidentity, with the first IMS server through the third RAT (e.g., RAT-3824) to establish the first call.

At operation 2408, the UE 702 maintains, under the second subscriberidentity, a connection with the second IMS server through the third RAT(e.g., RAT-3 824) when the first call is active.

FIG. 25 is a conceptual data flow diagram 2500 illustrating the dataflow between different components/means in an exemplary apparatus 2502.The apparatus 2502 may be a UE. The apparatus 2502 includes a receptioncomponent 2504, a decision component 2506, a communication managementcomponent 2508, a handover component 2512, and a transmission component2510.

The decision component 2506 determine a set of RATs available to the UE702 in accordance with a first subscriber identity (e.g., SIM1 702-1)associated with a first network (e.g., the mobile network 791) and asecond subscriber identity (e.g., SIM2 702-2) associated with a secondnetwork (e.g., the mobile network 792). In certain configurations, thefirst RAT is selected based on at least one of a call quality, a cost tomake the first call, a power consumption of the UE, and a handover rate.

The decision component 2506 determines whether the set includes a firstRAT accessing a base station (e.g., the base station 704-1) in the firstnetwork, a second RAT accessing a base station (e.g., the base station704-2) in the second network, and a third RAT accessing an access pointof a WLAN (e.g., the WLAN network 716).

When the set includes a first RAT accessing a base station in the firstnetwork, a second RAT accessing a base station in the second network,and a third RAT accessing an access point of a WLAN, then the method(process) proceeds to operation 1506, otherwise the method (process)ends.

The communication management component 2508 selects, in a firstperformance configuration, the first RAT to establish a first call underthe first subscriber identity (e.g., the SIM1 702-1).

The communication management component 2508 maintains, under the firstsubscriber identity, a connection with the first IMS server (e.g., theIMS service 714-1) through the first RAT.

The communication management component 2508 maintains, under the secondsubscriber identity, the connection with the second IMS server (e.g.,the IMS service 714-2) through the second RAT (e.g., the RAT-2 822).

The communication management component 2508 communicates, under thefirst subscriber identity, with a first IMS server (e.g., the IMSservice 714-1) of the first network through the first RAT to establishthe first call.

The handover component 2512 hands over the connection with the secondIMS server (e.g., the IMS service 714-2) from the second RAT to thefirst RAT or the third RAT.

The communication management component 2508 maintains, under the secondsubscriber identity, a connection with a second IMS server (e.g., theIMS service 714-2) of the second network through the first RAT (e.g.,the RAT-1 826) or the third RAT (e.g., the RAT-3 824) when the firstcall is active.

The communication management component 2508 receives, through the firstRAT and under the first subscriber identity, a call invitation toestablish the first call.

The communication management component 2508 selects, in a secondperformance configuration, the third RAT to establish the first callunder the first subscriber identity.

The handover component 2512 hands over the connection under the firstsubscriber identity with the first IMS server from the first RAT to thethird RAT (e.g., RAT-3 824).

The communication management component 2508 communicates, under thefirst subscriber identity, with the first IMS server through the thirdRAT (e.g., RAT-3 824) to establish the first call.

The decision component 2506 determines whether the connection under thesecond subscriber identity with the second IMS server is maintainedthrough the third RAT (e.g., RAT-3 824). If the connection under thesecond subscriber identity with the second IMS server is maintainedthrough the third RAT (e.g., RAT-3 824), then proceed to operation 1614,otherwise the method (process) ends.

The communication management component 2508 receives a call invitationto establish a second call under the second subscriber identity throughthe third RAT (e.g., RAT-3 824).

The communication management component 2508 holds the first call.

The handover component 2512 hands over the connection under the secondsubscriber identity with the second IMS server from the third RAT (e.g.,RAT-3 824) to the second RAT (e.g., RAT-2 822).

The communication management component 2508 communicates, under thesecond subscriber identity, with the second IMS server through thesecond RAT (e.g., RAT-2 822) to establish the second call.

The handover component 2512 hands over the holding of the first callfrom the first RAT to the third RAT.

The decision component 2506 determines whether the set includes thefirst RAT. If the set includes the first RAT, then the method (process)proceeds, otherwise the method (process) ends.

The communication management component 2508 communicates, under thefirst subscriber identity, with the first IMS server through the firstRAT to establish the first call.

The communication management component 2508 maintains, under the secondsubscriber identity, a connection with the second IMS server through thefirst RAT (e.g., RAT-1 826) when the first call is active.

The decision component 2506 determines whether the set includes thefirst RAT and the second RAT. If the set includes the first RAT and thesecond RAT, then the method (process) proceeds, otherwise the method(process) ends.

The communication management component 2508 communicates, under thefirst subscriber identity, with the first IMS server through the firstRAT to establish the first call.

The communication management component 2508 maintains, under the secondsubscriber identity, a connection with the second IMS server through thefirst RAT (e.g., RAT-1 826) when the first call is active.

The communication management component 2508 receives a call invitationto establish a second call under the second subscriber identity throughthe first RAT (e.g., RAT-1 826).

The communication management component 2508 holds the first call.

The handover component 2512 hands over the connection under the secondsubscriber identity with the second IMS server from the first RAT (e.g.,RAT-1 826) to the second RAT (e.g., RAT-2 822).

The communication management component 2508 communicates, under thesecond subscriber identity, with the second IMS server through thesecond RAT to establish the second call.

The handover component 2512 hands over the holding of the first callfrom the first RAT to the second RAT.

The decision component 2506 determines whether the set includes thesecond RAT. If the set includes the second RAT, then the method(process) proceeds to operation 2106, otherwise the method (process)ends.

The communication management component 2508 communicates, under thefirst subscriber identity, with the first IMS server through the secondRAT to establish the first call.

The communication management component 2508 maintains, under the secondsubscriber identity, a connection with the second IMS server through thesecond RAT (e.g., RAT-2 822) when the first call is active.

The decision component 2506 determines whether the set includes thefirst RAT and the third RAT. If the set includes the first RAT and thethird RAT, then the method (process) proceeds to operation 2206,otherwise the method (process) ends.

The communication management component 2508 communicates, under thefirst subscriber identity, with the first IMS server through the firstRAT to establish the first call.

The communication management component 2508 maintains, under the secondsubscriber identity, a connection with the second IMS server through thefirst RAT (e.g., RAT-1 826) or the second RAT (e.g., RAT-2 822) when thefirst call is active.

The decision component 2506 determines whether the set includes thesecond RAT and the third RAT. If the set includes the second RAT and thethird RAT, then the method (process) proceeds, otherwise the method(process) ends.

The communication management component 2508 communicates, under thefirst subscriber identity, with the first IMS server through the secondRAT or the third RAT (e.g., RAT-3 824) to establish the first call.

The communication management component 2508 maintains, under the secondsubscriber identity, a connection with the second IMS server through thesecond RAT (e.g., RAT-2 822) or the third RAT (e.g., RAT-3 824) when thefirst call is active.

The decision component 2506 determines whether the set includes thesecond RAT and the third RAT. If the set includes the second RAT and thethird RAT, then the method (process) proceeds, otherwise the method(process) ends.

The communication management component 2508 communicates, under thefirst subscriber identity, with the first IMS server through the secondRAT or the third RAT (e.g., RAT-3 824) to establish the first call.

The communication management component 2508 maintains, under the secondsubscriber identity, a connection with the second IMS server through thesecond RAT (e.g., RAT-2 822) or the third RAT (e.g., RAT-3 824) when thefirst call is active.

The decision component 2506 determines whether the set includes thethird RAT. If the set includes the third RAT, then the method (process)proceeds to operation 2406, otherwise the method (process) ends.

The communication management component 2508 communicates, under thefirst subscriber identity, with the first IMS server through the thirdRAT (e.g., RAT-3 824) to establish the first call.

The communication management component 2508 maintains, under the secondsubscriber identity, a connection with the second IMS server through thethird RAT (e.g., RAT-3 824) when the first call is active.

FIG. 26 is a diagram 2600 illustrating an example of a hardwareimplementation for an apparatus 2502′ employing a processing system2614. The apparatus 2502′ may be a UE. The processing system 2614 may beimplemented with a bus architecture, represented generally by a bus2624. The bus 2624 may include any number of interconnecting buses andbridges depending on the specific application of the processing system2614 and the overall design constraints. The bus 2624 links togethervarious circuits including one or more processors and/or hardwarecomponents, represented by one or more processors 2604, the receptioncomponent 2504, the decision component 2506, the communicationmanagement component 2508, the transmission component 2510, the handovercomponent 2512, and a computer-readable medium/memory 2606. The bus 2624may also link various other circuits such as timing sources,peripherals, voltage regulators, and power management circuits, etc.

The processing system 2614 may be coupled to a transceiver 2610, whichmay be one or more of the transceivers 254. The transceiver 2610 iscoupled to one or more antennas 2620, which may be the communicationantennas 252.

The transceiver 2610 provides a means for communicating with variousother apparatus over a transmission medium. The transceiver 2610receives a signal from the one or more antennas 2620, extractsinformation from the received signal, and provides the extractedinformation to the processing system 2614, specifically the receptioncomponent 2504. In addition, the transceiver 2610 receives informationfrom the processing system 2614, specifically the transmission component2510, and based on the received information, generates a signal to beapplied to the one or more antennas 2620.

The processing system 2614 includes one or more processors 2604 coupledto a computer-readable medium/memory 2606. The one or more processors2604 are responsible for general processing, including the execution ofsoftware stored on the computer-readable medium/memory 2606. Thesoftware, when executed by the one or more processors 2604, causes theprocessing system 2614 to perform the various functions described suprafor any particular apparatus. The computer-readable medium/memory 2606may also be used for storing data that is manipulated by the one or moreprocessors 2604 when executing software. The processing system 2614further includes at least one of the reception component 2504, thedecision component 2506, the communication management component 2508,the transmission component 2510, and the handover component 2512. Thecomponents may be software components running in the one or moreprocessors 2604, resident/stored in the computer readable medium/memory2606, one or more hardware components coupled to the one or moreprocessors 2604, or some combination thereof. The processing system 2614may be a component of the UE 250 and may include the memory 260 and/orat least one of the TX processor 268, the RX processor 256, and thecommunication processor 259.

In one configuration, the apparatus 2502/apparatus 2502′ for wirelesscommunication includes means for performing each of the operations ofFIG. 13 and FIG. 14. The aforementioned means may be one or more of theaforementioned components of the apparatus 2502 and/or the processingsystem 2614 of the apparatus 2502′ configured to perform the functionsrecited by the aforementioned means.

As described supra, the processing system 2614 may include the TXProcessor 268, the RX Processor 256, and the communication processor259. As such, in one configuration, the aforementioned means may be theTX Processor 268, the RX Processor 256, and the communication processor259 configured to perform the functions recited by the aforementionedmeans.

It is understood that the specific order or hierarchy of blocks in theprocesses/flowcharts disclosed is an illustration of exemplaryapproaches. Based upon design preferences, it is understood that thespecific order or hierarchy of blocks in the processes/flowcharts may berearranged. Further, some blocks may be combined or omitted. Theaccompanying method claims present elements of the various blocks in asample order, and are not meant to be limited to the specific order orhierarchy presented.

The previous description is provided to enable any person skilled in theart to practice the various aspects described herein. Variousmodifications to these aspects will be readily apparent to those skilledin the art, and the generic principles defined herein may be applied toother aspects. Thus, the claims are not intended to be limited to theaspects shown herein, but is to be accorded the full scope consistentwith the language claims, wherein reference to an element in thesingular is not intended to mean “one and only one” unless specificallyso stated, but rather “one or more.” The word “exemplary” is used hereinto mean “serving as an example, instance, or illustration.” Any aspectdescribed herein as “exemplary” is not necessarily to be construed aspreferred or advantageous over other aspects. Unless specifically statedotherwise, the term “some” refers to one or more. Combinations such as“at least one of A, B, or C,” “one or more of A, B, or C,” “at least oneof A, B, and C,” “one or more of A, B, and C,” and “A, B, C, or anycombination thereof” include any combination of A, B, and/or C, and mayinclude multiples of A, multiples of B, or multiples of C. Specifically,combinations such as “at least one of A, B, or C,” “one or more of A, B,or C,” “at least one of A, B, and C,” “one or more of A, B, and C,” and“A, B, C, or any combination thereof” may be A only, B only, C only, Aand B, A and C, B and C, or A and B and C, where any such combinationsmay contain one or more member or members of A, B, or C. All structuraland functional equivalents to the elements of the various aspectsdescribed throughout this disclosure that are known or later come to beknown to those of ordinary skill in the art are expressly incorporatedherein by reference and are intended to be encompassed by the claims.Moreover, nothing disclosed herein is intended to be dedicated to thepublic regardless of whether such disclosure is explicitly recited inthe claims. The words “module,” “mechanism,” “element,” “device,” andthe like may not be a substitute for the word “means.” As such, no claimelement is to be construed as a means plus function unless the elementis expressly recited using the phrase “means for.”

What is claimed is:
 1. A method of wireless communication of a userequipment (UE), comprising: determining a set of radio accesstechnologies (RATs) available to the UE in accordance with a firstsubscriber identity associated with a first network and a secondsubscriber identity associated with a second network; when the setincludes a first RAT accessing a base station in the first network, asecond RAT accessing a base station in the second network, and a thirdRAT accessing an access point of a wireless local area network (WLAN):maintaining, under the first subscriber identity, a connection with afirst IP Multimedia Subsystem (IMS) server through the first RAT;maintaining, under the second subscriber identity, a connection with asecond IMS server through the second RAT; selecting, in a firstperformance configuration, the first RAT to establish a first call underthe first subscriber identity; communicating, under the first subscriberidentity, with the first IMS server of the first network through thefirst RAT to establish the first call; switching to maintain, under thesecond subscriber identity, the connection with the second IMS server ofthe second network through the first RAT or the third RAT when the firstcall is active; receiving, through the first RAT and under the firstsubscriber identity, a call invitation to establish the first call;selecting, in a second performance configuration, the third RAT toestablish the first call under the first subscriber identity; handingover the connection under the first subscriber identity with the firstIMS server from the first RAT to the third RAT; and communicating, underthe first subscriber identity, with the first IMS server through thethird RAT to establish the first call.
 2. The method of claim 1, whereinthe first RAT is selected based on at least one of a call quality, acost to make the first call, a power consumption of the UE, and ahandover rate.
 3. The method of claim 1, further comprising: subsequentto the communicating with the first IMS server to establish the firstcall: handing over the connection with the second IMS server from thesecond RAT to the first RAT or the third RAT.
 4. The method of claim 1,wherein the connection under the second subscriber identity with thesecond IMS server is maintained through the first RAT or the third RAT,the method further comprising: receiving a call invitation to establisha second call under the second subscriber identity through the thirdRAT; holding the first call; handing over the connection under thesecond subscriber identity with the second IMS server from the first RATor the third RAT to the second RAT; and communicating, under the secondsubscriber identity, with the second IMS server through the second RATto establish the second call.
 5. The method of claim 4, furthercomprising: handing over the holding of the first call from the firstRAT to the second RAT or the third RAT.
 6. The method of claim 1,further comprising when the set includes the first RAT: communicating,under the first subscriber identity, with the first IMS server throughthe first RAT to establish the first call; and maintaining, under thesecond subscriber identity, a connection with the second IMS serverthrough the first RAT or the third RAT when the first call is active. 7.The method of claim 1, further comprising when the set includes thefirst RAT and the second RAT: communicating, under the first subscriberidentity, with the first IMS server through the first RAT to establishthe first call; and maintaining, under the second subscriber identity, aconnection with the second IMS server through the first RAT when thefirst call is active.
 8. The method of claim 7, further comprising:receiving a call invitation to establish a second call under the secondsubscriber identity through the first RAT; holding the first call;handing over the connection under the second subscriber identity withthe second IMS server from the first RAT to the second RAT; andcommunicating, under the second subscriber identity, with the second IMSserver through the second RAT to establish the second call.
 9. Themethod of claim 8, further comprising: handing over the holding of thefirst call from the first RAT to the second RAT.
 10. The method of claim1, when the set includes the second RAT: communicating, under the firstsubscriber identity, with the first IMS server through the second RAT toestablish the first call; and maintaining, under the second subscriberidentity, a connection with the second IMS server through the second RATwhen the first call is active.
 11. The method of claim 1, when the setincludes the first RAT and the third RAT: communicating, under the firstsubscriber identity, with the first IMS server through the first RAT toestablish the first call; and maintaining, under the second subscriberidentity, a connection with the second IMS server through the first RATor the third RAT when the first call is active.
 12. The method of claim1, when the set includes the second RAT and the third RAT:communicating, under the first subscriber identity, with the first IMSserver through the second RAT or the third RAT to establish the firstcall; and maintaining, under the second subscriber identity, aconnection with the second IMS server through the second RAT or thethird RAT when the first call is active.
 13. The method of claim 1, whenthe set includes the third RAT: communicating, under the firstsubscriber identity, with the first IMS server through the third RAT toestablish the first call; and maintaining, under the second subscriberidentity, a connection with the second IMS server through the third RATwhen the first call is active.
 14. An apparatus for wirelesscommunication, the apparatus being a user equipment (UE), comprising: amemory; and at least one processor coupled to the memory and configuredto: determine a set of radio access technologies (RATs) available to theUE in accordance with a first subscriber identity associated with afirst network and a second subscriber identity associated with a secondnetwork; when the set includes a first RAT accessing a base station inthe first network, a second RAT accessing a base station in the secondnetwork, and a third RAT accessing an access point of a wireless localarea network (WLAN): maintain, under the first subscriber identity, aconnection with a first IP Multimedia Subsystem (IMS) server through thefirst RAT; maintain, under the second subscriber identity, a connectionwith a second IMS server through the second RAT; select, in a firstperformance configuration, the first RAT to establish a first call underthe first subscriber identity; communicate, under the first subscriberidentity, with the first IMS server of the first network through thefirst RAT to establish the first call; switch to maintain, under thesecond subscriber identity, a connection with a second IMS server of thesecond network through the first RAT or the third RAT when the firstcall is active; receive, through the first RAT and under the firstsubscriber identity, a call invitation to establish the first call;select, in a second performance configuration, the third RAT toestablish the first call under the first subscriber identity; hand overthe connection under the first subscriber identity with the first IMSserver from the first RAT to the third RAT; and communicate, under thefirst subscriber identity, with the first IMS server through the thirdRAT to establish the first call.
 15. The apparatus of claim 14, whereinthe first RAT is selected based on at least one of a call quality, acost to make the first call, a power consumption of the UE, and ahandover rate.
 16. A non-transitory computer-readable medium storingcomputer executable code for wireless communication of a user equipment(UE), comprising code to: determine a set of radio access technologies(RATs) available to the UE in accordance with a first subscriberidentity associated with a first network and a second subscriberidentity associated with a second network; when the set includes a firstRAT accessing a base station in the first network, a second RATaccessing a base station in the second network, and a third RATaccessing an access point of a wireless local area network (WLAN):maintain, under the first subscriber identity, a connection with a firstIP Multimedia Subsystem (IMS) server through the first RAT; maintain,under the second subscriber identity, a connection with a second IMSserver through the second RAT; select, in a first performanceconfiguration, the first RAT to establish a first call under the firstsubscriber identity; communicate, under the first subscriber identity,with the first IMS server of the first network through the first RAT toestablish the first call; switch to maintain, under the secondsubscriber identity, a connection with a second IMS server of the secondnetwork through the first RAT or the third RAT when the first call isactive; receive, through the first RAT and under the first subscriberidentity, a call invitation to establish the first call; select, in asecond performance configuration, the third RAT to establish the firstcall under the first subscriber identity; hand over the connection underthe first subscriber identity with the first IMS server from the firstRAT to the third RAT; and communicate, under the first subscriberidentity, with the first IMS server through the third RAT to establishthe first call.